1Chef's Note: If you don't want to use fresh tomatoes, get a 14 ounce (0.4 liter) can of tomatoes, petite diced, and drain them.
In the United States, I prefer Hunt's Petite Diced tomatoes.
2Add all the ingredients, except the olive oil, and the onions, to the bowl of a food processor, fitted with an S-blade.
3Chef's Tip: Watch the liquid content of the fresh or canned tomatoes, and make sure that most of the additional liquid is strained before adding them to the food processor.
4Pulse until throughly combined.
5Add the onion, and blend until the onion is totally blended into the mixture.
6Chef's Note: Two of the twists in this recipe are that I'm using tomatoes instead of ketchup, and I'm using olive oil; as opposed to vegetable oil.
7Chef's Note: You can't over blend this thing. Keep blending until the onion is liquified into the dressing.
8Turn the food processor on high, and slowly drizzle the olive oil into the dressing. The key here is to add the olive oil slowly.
9Place into a covered container and let rest in the refrigerator for 24 hours before using.
10Chef's Note: This dressing is a bit more runny than the store-bought kind. I make my dressing so that I can spoon some into a bowl with the other ingredients (lettuce, etc), and then toss the dressing with the salad.
I don't like pouring a thick glop of dressing onto salads.